641 research outputs found
Does the detection of X-ray emission from SN1998bw support its association with GRB980425?
We show that the recent identification of X-ray emission from SN1998bw is
naturally explained as synchrotron emission from a shock driven into the wind
surrounding the progenitor by a mildly relativistic shell ejected by the
supernova, the existence of which was inferred earlier from radio observations.
X-ray observations imply a shell energy E~10^{49.7}erg, and constrain the
initial shell velocity \beta*c and normalized wind mass loss rate,
\dot{m}=(\dot{M}/10^{-5}M_sun/yr)/(v_w/10^3 km/s), to satisfy
\beta^3*\dot{m}~10^{-1.5}. The inferred energy is consistent with energy
estimates based on radio observations provided \dot{m}~0.04, in which case
radio observations imply \beta~0.8, consistent with the X-ray constraint
\beta^3*\dot{m}~10^{-1.5}. While X-ray observations allow to determine the
parameters characterizing the pre-explosion wind and the mildly relativistic
shell ejected by SN1998bw, they do not provide evidence for existence of an
off-axis "standard" GRB jet associated with SN1998bw, that may have produced
GRB980425. However, as recently pointed out in (astro-ph/0310320), the lack of
observational signatures typically expected to be produced by such an off-axis
jet on a 1yr time scale, may be due to a low \dot{m}<0.1, which implies that an
off-axis jet will become observable only on >10yr time scale.Comment: Minor changes. Accepted to ApJ
Gamma-burst emission from neutron-star accretion
A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without a magnetic field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to relatively small charge separation is required to drag electrons into the star with the nuclei against the flux of photons leaking out through the accreting matter. The photon number is not increased substantially by Bremsstrahlung or any other process. It is suggested that instability in an accretion disc might provide the infalling matter required
Measurements at the southern magnetic conju- gate region of the fission debris from the starfish nuclear detonation
Measurement of fission products from Star Fish high-altitude nuclear explosion with recording gamma-ray spectromete
A Systematic Analysis of Supernova Light in Gamma-Ray Burst Afterglows
We systematically reanalyzed all Gamma-Ray Burst (GRB) afterglow data
published through the end of 2002, in an attempt to detect the predicted
supernova light component and to gain statistical insight on its
phenomenological properties. We fit the observed photometric light curves as
the sum of an afterglow, an underlying host galaxy, and a supernova component.
The latter is modeled using published multi-color light curves of SN 1998bw as
a template. The total sample of afterglows with established redshifts contains
21 bursts (GRB 970228 - GRB 021211). For nine of these GRBs a weak supernova
excess (scaled to SN 1998bw) was found, what makes this to one of the first
samples of high-z core collapse supernovae. Among this sample are all bursts
with redshifts less than ~0.7. These results strongly support the notion that
in fact all afterglows of long-duration GRBs contain light from an associated
supernova. A statistics of the physical parameters of these GRB-supernovae
shows that SN 1998bw was at the bright end of its class, while it was not
special with respect to its light curve shape. Finally, we have searched for a
potential correlation of the supernova luminosities with the properties of the
corresponding bursts and optical afterglows, but we have not found such a
relation.Comment: 25 pages, 7 figures, accepted by ApJ; revised, shortened and updated
compared to version 1; Title slightly changed; all figures showing individual
afterglow light curves removed, as advised by the referee; conclusions
unchange
The difficulty of ultraviolet emssion from supernovae
There are certain conceptual difficulties in the theory of the generation of ultraviolet radiation which is presumed for the creation of the optical fluorescence mechanism of supernova light emission and ionization of a nebula as large as the Gum nebula. Requirements concerning the energy distribution of the ultraviolet photons are: 1) The energy of the greater part of the photons must be sufficient to cause both helium fluorescence and hydrogen ionization. 2) If the photons are emitted in an approximate black body spectrum, the fraction of energy emitted in the optical must be no more than what is already observed. Ultraviolet black body emission depends primarily on the energy source. The probability that the wide mixture of elements present in the interstellar medium and supernova ejecta results in an emission localized in a limited region with less than 0.001 emission in the visible, for either ionization or fluorescence ultraviolet, is remote. Therefore transparent emission must be excluded as unlikely, and black body or at least quasi-black-body emission is more probable
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